The use of laser-generated electromagnetic optical energy has become ubiquitous in applications ranging in areas from commercial to national defense. An illustrative example of the former is the use of optical energy for industrial materials processing, including cutting, welding and surface treatment. End products resulting from such implementations come from such wide ranging business areas as automotive, aerospace, appliance and shipbuilding. More exotic applications can include rock drilling for mining and/or oil and gas exploration purposes. Directed energy or so-called “laser weapons” are finding increased acceptance in the defense community because of the position-sensitive lethality delivery. As lasers become smaller, more efficient and robust, it becomes easier to integrate them into ground-based, sea-based, airborne and space-borne paradigms, thereby further increasing the need for improved lasers and laser components.
Components found in typical lasers include a pump radiation source, a lasing medium, and a resonating cavity. A laser is conventionally classified according to its type of active (i.e. lasing) medium. Several conventional types of lasers include gas lasers, semiconductor lasers, solid-state lasers, excimer lasers, dye lasers and the like. Solid-state lasers (SSLs), for example, have received renewed attention in recent years, especially in high average power (HAP) applications, where large energy delivery allows for implementation in military and/or industrial uses. SSLs typically include a solid-state host material in either crystal or glass form that is doped with suitable rare-earth ions to produce stimulated emissions of light. These ions are optically pumped with light generated by another optical source, such as a semiconductor diode or high intensity flashlamp. After absorption of the pumping light, the ions re-emit the light into the optical resonator, creating a coherent light or laser output. As mentioned above, different types of lasers function in a similar manner, but with different lasing materials.
Diode lasers, generally speaking, are compositionally the same as one or more light emitting diodes. In order for the diode to emit light, electrons are injected into the semiconductor in the conduction band. When the electrons change from the conduction band to the valence band, they emit light, although this light is incoherent without a resonating cavity. In order for a light emitting diode to produce coherent light, the diode semiconductor is placed inside a resonator cavity. The laser light produced can be used for any purpose. Diode lasers have been used, for example, in optical communications systems, as well as in solid state or other lasers as pump light sources.
While diode lasers are generally highly efficient and robust, their usefulness in many applications is limited by the relatively low power of the beam produced. The power may be increased by using multiple diodes to produce beams of a common frequency and phase. Multiple laser diodes, for example, could be used to simultaneously provide pump radiation to a gain medium of a solid state or other laser. Multiple diode lasers could also be used to create a high power beam directly from the semiconductor diodes. In order to accomplish this, the phases of the individual diodes need to be coupled or synchronized with one another. Most commonly, this is accomplished by incorporating a passive optical element that provides a small amount of optical feedback between the individual diodes. While this technique has been employed with some success, the number of diodes that can be coupled together with purely passive elements has been limited in practice by phase differences in light produced by the multiple sources. That is, variations in phase across the wavefront of the resultant beam have restricted the number of diodes that may be simultaneously used in the light source. A tradeoff therefore exists between the power and the phase coherence of the beam, with increases in one resulting in decreases in the other.
It is therefore desirable to create a laser light source capable of producing a high power yet phase synchronous beam of light. It is also desirable to create techniques for operating a light source that produces a high-energy beam. Other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background discussion.